This application claims the priority of Application No. H09-263533, filed Sep. 29, 1997 in Japan, the subject matter of which is incorporated herein by reference.
The present invention relates to a method and a system for emulating a computer-controlled apparatus, such as a microcomputer application system.
In general, an in-circuit emulator is designed to cause a computer to behave as if it were another component. Emulators are used in computer development for enabling existing hardware and software to simulate the computer that is under development.
A conventional in-circuit emulator is arranged between a parent calculating apparatus, such as a PC (Personal Computer), and a microcomputer application system to be evaluated. The microcomputer application system includes a microcomputer. The in-circuit emulator includes a simulation circuit to simulate the operation of the microcomputer, including a central processing unit (CPU), a random access memory (RAM), and peripheral circuits. The simulation circuit is formed on a simulator chip.
The in-circuit emulator further includes a designator unit, which is realized with a RAM or the like, behaving like a read-only memory (ROM) in the microcomputer application system. The designator unit supplies instruction signals or control signals to the simulator chip.
In such an in-circuit emulator, a supply voltage, for example 5 V, is usually applied to the simulator chip and to the designator unit. In another case, another level of supply voltage, for example 3 V, is applied in common to the simulator chip and to the microcomputer application system.
According to the conventional in-circuit emulator, when the same level of supply voltage V is applied to the simulator chip and the designator unit, the supply voltage to be applied to the microcomputer application system is also equalized to the supply voltage V. If the supply voltage to be applied to the microcomputer application system is different from the supply voltage V, it is necessary to provide a voltage level shift circuit between the in-circuit emulator and the microcomputer application system.
The level shift circuit may cause off-timing problems; and therefore, the results of emulation (simulation) may be different from those of the actual operation of the microcomputer application system.
On the other hand, when the supply voltage V for the simulator chip is designed to be identical to the supply voltage applied to the microcomputer application system, it is necessary to provide a voltage level shift circuit between the designator unit and the simulator chip. Between the designator unit and the simulator chip, signals must be transferred at a high speed. The voltage level shift circuit may slow the operating speed of the in-circuit emulator. As a result, reliability of the emulation decreases.
Accordingly, an object of the invention is to provide a method in which a computer-controlled apparatus is emulated with a high reliability.
Another object of the invention is to provide an emulation system with which a computer-controlled apparatus is emulated with a high reliability.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
According to a first aspect of the invention, a second supply voltage is applied in common to a computer-controlled apparatus and to a first block of a simulator, while a first supply voltage is applied in common to a designator unit and to a second block of the simulator. The operation of the computer-controlled apparatus is simulated by the simulator in response to instruction signals supplied from the designator unit.
According to a second aspect of the invention, an emulator includes a designator unit that supplies instruction signals for simulation and a simulator that simulates the operation of a computer-controlled apparatus. The simulator includes a first block connected to the designator unit and a second block connected to the designator unit. The emulator further includes a first power supply that applies a first voltage to the computer-controlled apparatus and to the first block of the simulator in common; and a second power supply that applies a second voltage to the designator unit and to the second block of the simulator in common. The simulator simulates the operation of the computer-controlled apparatus in response to instruction signals supplied from the designator unit.
The emulator may further include a level shifter that converts the voltage level of signals transmitted between the first block and second block of the simulator. Otherwise, in the emulator, the first block of the simulator may include an input circuit of a TTL (Transistor-Transistor Logic) gate and an output circuit of a CMOS (Complementary Metal-Oxide Semiconductor) transistor. In addition, the second block of the simulator may include an input circuit of a TTL (Transistor-Transistor Logic) gate and an output circuit of a CMOS (Complementary Metal-Oxide Semiconductor) transistor. The output circuit of the first block of the simulator is connected to the input circuit of the second block of the simulator, and the input circuit of the first block of the simulator is connected to the output circuit of the second block of the simulator.